1. Field of the Invention
The present invention pertains to the art of cooking appliances and, more particularly, to a preheat system employed to eliminate byproducts from an oven cavity between cleaning cycles in a convection cooking appliance.
2. Discussion of the Prior Art
Conventional cooking appliances generally perform cooking operations through radiant heating developed from bake and/or broil elements. Such types of cooking appliances can take various forms, mainly ranges and wall ovens. When utilizing a conventional cooking appliance, the oven is initially controlled to proceed through a preheat cycle wherein both the bake and broil elements are actuated in order to reach a desired cooking temperature. Often times, a signal is provided to a user when the preheat cycle is complete in order to indicate when the food to be cooked can be placed in the oven. During these preheat operations, retained grease, oils, other hydrocarbon compounds or the like, herein collectively referred to as byproducts, contained in the oven cavity from prior cooking operations will be, at least partially, burnt which can create smoke and byproduct laden air.
Certain known types of cooking appliances incorporate internal fans which operate during certain cooking periods. Therefore, these known cooking appliances can perform convection cooking operations. Convection cooking is actually more prevalent in microwave and other types of ovens which do not require preheating. However, utilizing convection heating in a cooking appliance including more conventional elements used to perform preheat and cooking operations is also known. In these types of cooking appliances, the convection air flow can actually increase the negative effects of any smoke and byproduct containing air, particularly in situations where a door of the oven cavity being preheated is opened.
To at least address the concerns raised above, there exists a need in the art of cooking appliances, specifically convection cooking appliances, for a more effective preheating system whereby retained greases, oils, other hydrocarbon compounds, and the like remaining from prior cooking operations can be effectively eliminated, while minimizing any negative effects of developed smoke and other airborne byproducts.
In accordance with the invention, a preheat system for a convection cooking appliance functions to control the operation of multiple heating units, the heating of a catalyst, and the speed of a blower assembly of the appliance to effectively eliminate grease, oils, and other hydrocarbon compounds remaining from prior cooking operations, while minimizing is the generation of any appreciable amount of smoke, between successive self-cleaning operations. In accordance with a preferred embodiment of the invention, at least one of the heating units is energized, preferably at full power, and the blower assembly is run at a low to moderate speed when a cooking operation is selected. Once the catalyst reaches a critical temperature, e.g., 450xc2x0 F., another one of the heating unit is initiated under full power and/or 100% duty cycle.
At this point, the grease, oils, other hydrocarbons, and the like byproducts remaining from prior cooking operations will begin combusting, thereby generating some smoke, a majority of which is forced out through the catalyst. Because the catalyst has been sufficiently heated, the fats, oils and other hydrocarbons can be completely combusted and converted to carbon dioxide and water with very little or no smoke. As the catalyst reaches a critical firing temperature, additional combustion of the grease, oils and other hydrocarbons will commence. Therefore, in this manner, the combustion of the remaining byproducts is performed in various, controlled stages. At this point, the speed of the blower assembly is increased to draw additional oxygen into the oven cavity in order to maintain an oxidizing atmosphere.
Additionally, if a door for oven cavity is opened during the cycle, the blower assembly remains ON, but is controlled to operate at a lower speed, preferably in the order of 20%, to create air circulation in the oven cavity. In this manner, the blower assembly creates a negative pressure differential in the oven cavity such that any smoke will be drawn back into the oven cavity, instead of being released into the ambient atmosphere. In addition, the creation of the pressure differential actually functions to draw in more oxygen so as to enable even further combustion.
Additional objects, features and advantages of the present invention will become readily apparent from the following detailed description of a preferred embodiment thereof, when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views.